The proposed research plan is in response to RFA-DK-11-001, "A Genitourinary Anatomy Project (GUDMAP)." This continuation of the GUDMAP initiative (GUDMAP II) aims to define the molecular anatomy of the lower urinary tract. We propose to generate a series of novel mouse strains that will enable groups funded through this RFA to identify, isolate, and genetically manipulate target cell types to better understand the roles of these cells and their descendants in development of the lower urinary tract. We anticipate that the strains will enable antibody-based approaches for 2- and 3-dimensional imaging of organ anatomy, cell isolation for transcriptional analysis of gene expression, and cell fate analysis to explore cell relationships in developing and adult organs of the lower urinary tract. In Aim1, we will make use of the extensive repertoire of targeted embryo stem (ES) cells created by the NIH-funded KOMP initiative and its European counterpart, EUCOMM. These "knock-out first conditional alleles" will serve as a platform for secondary gene-targeting, utilizng a dual recombinase mediate cassette exchange approach. In this, novel cell markers (GPP) and genome modifying enzymes (CRE-ERT2) are placed under the control of specific genes selected for expression in cell populations of interest. In Aim 2, targeted ES cells will be used t generate chimeric mice and ultimately novel mouse strains harboring the new marker/modifier alleles. These strains will be distributed to GUDMAP II members to facilitate their analyses and to NIH-funded Mouse Mutant Resource Centers for distribution to the biomedical research community.